Exhaust nozzles are used on business and commercial aircraft for reducing the noise produced by the engine at take-off, as well as for optimizing the aircraft take-off, climb and cruise performance, and for decelerating the aircraft at landing.
Variable area exhaust nozzles are known in the art. For example, U.S. Pat. No. 5,221,048 describes a variable exhaust area nozzle comprising a fixed structure or nacelle on which are hinged two pivoting half shells or nacelle extensions including an exit nozzle that cooperate radially and longitudinally with the nacelle. Fluid tightness between the two half shells and the fixed part is ensured through a sealing arrangement. Actuating means control the opening position of the shells to their fully opened position or to their fully closed position or to any intermediate position, allowing the adjustment of the nozzle exhaust area to the particular value required for achievement of optimum performance for the particular flight conditions.
The system described in patent ""048 is advantageous because it has a relatively low number of moving parts, and at the same time it allows the area variation of the exhaust of the nozzle. Therefore, at take-off, with the variable nozzle opened, meaning that the value of the nozzle throat area is increased, the noise generated by the engine is decreased. During climb, with the variable nozzle closed, meaning that the nozzle throat area is reduced to its minimum value, climb performance is improved, and at cruise with the variable nozzle set to its nominal position, cruise performance is optimized.
However, the adjustments of the two shells that control the value of the area of the throat of the variable nozzle to any position between its two extreme positions, necessitate the use of actuating means with rather sophisticated control logic if the adjustments are fully integrated to the engine computer. This has a direct consequence of increasing the cost of the technology. Also, when the shells move away from their nominal position, they modify the outer mold line (OML) of the rear part of the nacelle.
While, from a performance point of view, this is not critical, as when this happens, the aircraft is at rather low speed, and for cosmetic reasons it is desirable that the OML not be altered by the operation of the variable nozzle. Also, while the variable nozzle described in patent ""048 is attractive and readily applicable to business aircraft using engine with long nacelle, it has been found that it is more difficult to use this technology on short nacelle, a more commonly used installation on commercial aircraft.
Another limiting factor to the use of the variable nozzle described in patent ""048 is that it is difficult to integrate it on a nacelle equipped with a target type thrust reverser and that its delta weight with a fixed nozzle tends to increase as the engine thrust category is greater than 40,000 pounds.
In order to reduce the landing distance of a turbofan engine powered aircraft as well as to increase the level of safety when the aircraft is landing on a wet or icy runway, thrust reversers are utilized to re-direct forward the flow of engine exhaust gases in order to provide a braking thrust for the aircraft.
There are basically two main types of thrust reversers used on turbofan engines. A first type reverses the total mass flow, core and fan flows, while the second type reverses the fan flow only.
As disclosed in the detailed description, the variable exhaust nozzle according to the present invention is applicable to both types of thrust reversers. The exhaust nozzle can be installed on nacelles of turbofan engines that are fitted on the fuselage or under the wings of an aircraft. The nacelles may or may not be equipped with a thrust reverser, and they can be of the long, short, or C-duct types.
Typically, the thrust reversers that reverse the total mass flow of the engine are more commonly called target reversers or pivoting doors reversers, and are generally composed of at least a pair of thrust reverser doors capable of pivoting about axes which are substantially transverse to the axis of the engine, between a stow position for forward thrust and deploy position for reverse thrust. While most of these target reversers constitute a portion of the exhaust nozzle when they are in their stow configuration, very few of them have the capability for adjustment of the throat of the exhaust nozzle for optimizing the aircraft performance during take-off climb and cruise, or for reducing the noise emitted by the engine during take-off.
Typical examples of target or pivoting door reversers are described in U.S. Pat. Nos. 5,779,192, 5,826,823, 5,819,527 and 5,875,995. In U.S. Pat. No. 5,779,192, the depicted apparatus has two reverser doors 17a, 17b which are pivotally mounted respectively about stationary axis 18a, 18b. With the reverser doors in the stow position, they form the exhaust nozzle for the engine gases, and the throat is not adjustable and is located at the trailing edge 19 of the reverser doors.
In U.S. Pat. No. 5,826,823, typical of a pivoting doors type reverser, the apparatus has a fixed structure that cooperates with at least two reverser doors 26, 28. The fixed structure 20 includes side beams 22 that terminate in an annular aft portion 24. It is the fixed annular portion 24 that forms the exhaust nozzle for the jet engine, and the nozzle throat located at the trailing edge of the fixed portion is not adjustable.
In U.S. Pat. No. 5,819,527, the structural composition of the apparatus is very similar to U.S. Pat. No. 5,779,192, i.e., the exhaust nozzle is formed by an aft fixed, non-adjustable structure 3. In U.S. Pat. No. 5,875,995, a fixed non-adjustable rear annular portion 34 forms the exhaust nozzle.
A typical example of a target reverser with throat adjustment capability is described in U.S. Pat. No. 5,181,676. When the reverser doors 30 are stowed, a pair of shells 44 that cooperates with the pair of thrust reverser doors forms the exhaust nozzle. The pivots 40 of the reverser doors, which are linked to the corresponding pivots 58 of the shells via arms 56, have the capability of undergoing a radial and longitudinal displacement that confers the adjustment of the area to the throat of the exhaust nozzle.
While this arrangement is attractive by its simplicity, the amount of throat area variation capability is limited to about 10% over the nominal value. The limitation is a consequence of the mechanical arrangement that necessitates, in forward thrust, the radial and longitudinal displacement of the thrust reverser doors so that the throat area of the exhaust nozzle can be adjusted to the desired value. Also, when the reverser doors and shells move away from their nominal position, they modify the outer mold line of the rear part of the nacelle.
While, from a performance point of view, this is not critical, as when this happens, the aircraft is at rather low speed, and for cosmetic reasons it is desirable that the OML be not altered by the operation of the variable nozzle. Also, while the thrust reverser with variable nozzle described in patent ""676 is attractive and readily applicable to business aircraft using engine with long nacelle, it has been found that it is more difficult to use this technology on short nacelle, a more commonly used installation on commercial aircraft.
Typically, the thrust reversers that reverse the fan flow only can be classified into three main groups: the cascades type, the pivoting doors type and the fan reverse pitch mode type. With reference to the cascades type, for example, U.S. Pat. Nos. 3,779,010, 4,922,713 and 5,655,360 show a cascades type fan thrust reverser with a variable nozzle for the fan flow only. A cascades type fan thrust reverser function and operation being well known in the art, no further comments will be offered on that particular aspect.
However, it is important to concentrate on the variable nozzle portion of these fan reversers to understand the novelty of the present invention. As shown in U.S. Pat. Nos. 3,779,010 and 4,922,713, the increasing of the fan exit area is achieved through the axial separation of a downstream structure with relation to an upstream structure.
It is this axial separation between the downstream and upstream structures that creates the opening so that a portion of the fan flow can be directed through the opening to increase the fan flow exit area. Also, when the downstream and upstream structures are axially separated, the portion of the fan flow that exits through the created opening necessitates the use of rather sophisticated devices for promoting the attachment of the flow portion to the outer surface of the downstream structure.
In U.S. Pat. No. 5,655,360, the increasing of the fan exit area is achieved through the axial rearward translation of an aft cowl 34 that cooperates with a fixed core cowl 22, and the thrust reverser function is achieved by the further rearward axial displacement of cowl 34 that uncovers the cascades 42 and deploy the blocker doors 44. While the variable nozzle performance of this patent is most certainly more efficient than what is described in U.S. Pat. Nos. 3,779,010 and 4,922,713, it has still the drawback of having the thrust reverser function and the variable nozzle function achieved via the axial rearward translation of the same structure. This in turn necessitates the use of additional retention devices with rather sophisticated control logic to prevent inadvertent in-flight deployment of the reverser.
In another example, U.S. Pat. No. 5,778,659 shows a fan reverser with a variable exhaust nozzle. While the technology described in this patent is an improvement over the prior art, since now the variable nozzle function is segregated from the thrust reverser function, it still requires the rearward axial translation of a sleeve 38 that cooperates with the fixed core cowl 26. The required associated tracks and actuation system contribute to increasing the weight of the overall installation.
With reference to the second group of fan reversers, i.e., the pivoting doors type, U.S. Pat. Nos. 4,922,712, 5,863,014, 5,913,476, 5,934,613, 6,101,807, for example, show that these reversers are generally composed of a plurality of doors hinged on a fixed structure. The fixed structure has a downstream end that forms the exhaust nozzle for the fan flow, and the exhaust nozzle has no capability for throat area adjustment.
With reference to U.S. Pat. No. 5,853,148, the exhaust nozzle of the fan reverser has throat area adjustment capability. Adjustment of the value of the throat area of the fan nozzle is achieved through the rearward axial displacement of an annular structure 15 that cooperates with a fixed core cowl 11 via guiding tracks 17, 18. This arrangement has the drawback of increasing the weight of the installation because of the required additional movable structure with its associated guiding tracks and actuation system.
With reference to the third group of fan reversers, i.e., the fan reversing pitch, U.S. Pat. No. 3,820,719 shows that, in forward thrust, the adjustment of the value of the throat of the fan nozzle is achieved through the rearward and axial displacement of an annular structure 20 that cooperates with a fixed structure 24 via guiding tracks 19, and that reverse thrust is achieved by further rearward displacement of the, same, annular structure combined with the reversing of the pitch of the fan.
While it is advantageous to provide a larger exit area for the nozzle flow at take-off and during part of climb, the above systems are based on the rearward axial translation of a structure with associated translating tracks and actuation system, for creating the required opening to the fan flow in direct thrust and for uncovering the cascades and deploying in the fan duct of a plurality of blocker doors for reverse thrust operation. This in turn leads to a significant additional weight that is detrimental to the overall performance of the aircraft.
Aircraft noise pollution is becoming a major environmental concern for the world community. The Federal Aviation Administration (FAA) is responding to this concern by imposing more stringent noise restrictions for aircraft certification than ever before. Research and development of noise-reduction technology is underway for newer engines and for retrofitting existing engines so that they are as quiet as, or quieter than, required. By using laser Doppler velocimetry technology, it is possible to perform a comprehensive detailed analysis of the jet exhaust turbulence and internal velocity fields of the jet flows.
Noise suppressors in current use are revising the noise pattern by changing primarily the vibration frequency of the noise created by the engine exhaust. For long nacelles, these noise suppressors consist primarily of ordinary jet nozzles that have a special configuration: they consist mainly of multi-lobes that are forming the exhaust of the engine core hot flow. This multi-lobes exhaust nozzle type, also called mixer nozzle, is installed on the turbine exhaust casing, and is surrounded by the by-pass fan airflow. Their objective, for improved performance and reduced jet noise, is to ensure the mixing of the turbofan engine core and fan subsonic flows, prior to their fixed, non-adjustable, common exhaust.
The jet noise is reduced with improved internal exhaust gas mixers. The laser Doppler velocimetry measurements at the fixed common exhaust nozzle shows the presence of high-velocity regions at the common nozzle exit. These regions directly correspond to the particular configuration of the mixer lobes. This means that there are as many high-velocity regions as there are lobes on the mixer.
While tests show that the number of lobes on a mixer does not greatly affect the radial mean velocity, tests also show that the turbulence intensity, with respect to the centerline velocity, is lower for a higher number of lobes mixer. Tests also show that the radial mean velocity, with mixer nozzles, is reduced compared to a non-mixer core nozzle. As a direct consequence of the reduction of the mean jet exhaust velocity, the acoustic data shows that mixer nozzles are quieter than non-mixer core nozzles. The high frequency noise is the result of the mixing between the hot core flow and the cold fan flow within the structure of the fixed common exhaust nozzle. Acoustic tests show that the higher the number of lobes on a mixer, the lower high frequency mixing noise.
When the exit area of the common exhaust of the hot core flow and the cold fan flow is adjustable, acoustic tests, on real turbofan engine, demonstrate that the noise is further reduced compared to a non-adjustable exit area of the common exhaust. This is true whether the core nozzle is of a mixer type or not. However, the greatest noise reduction is achieved when both flows are mixed within the common exhaust nozzle, and with the exit area of the common exhaust nozzle increased. The opening of the exit area of the common exhaust further reduces the vibration frequency of the noise created by the engine exhaust.
Although the laser Doppler velocimetry measurements at the adjustable exit of the common exhaust was not used for these real engine acoustic tests, it is more than likely that the previously described high-velocity regions at the common nozzle exit are still present. These regions, as for a fixed common exhaust nozzle, directly correspond to the particular configuration of the mixer lobes. This means that there are still as many high-velocity regions as there are lobes on the mixer. However, with comparison to a non-adjustable common exhaust, since tests demonstrate a significant reduction in noise, this means that the velocity of the high-velocity regions as well as the radial mean velocity are most certainly decreased when the exit of the common exhaust is increased.
As a direct consequence of the reduction of the velocities, the acoustic data shows that a mixer nozzle combined with an adjustable common exhaust is significantly quieter than the same mixer nozzle combined with a non-adjustable common exhaust or quieter than a non-mixer core nozzle. The consequence of the combination mixer nozzle and adjustable common exhaust is that the high frequency noise, a result of the mixing between the hot core flow and the cold fan flow within the structure of the common exhaust nozzle, is decreased when the exit area of the adjustable common exhaust is increased.
This technology has matured to the extent that it has been ground tested on a large commercial turbofan engine and a small turbofan engine for business aircraft. It has been also flown tested on a business aircraft. Noise reduction data is significant. However, to this point, the exit area of the common exhaust nozzle for long nacelle has been infinitely adjustable between two extreme positions.
While in some cases this infinite adjustment capability may be desirable for optimum performance, in other cases it may be sufficient to somewhat limit the adjustment capability. If the primary goal is to reduce noise at take-off, then the technology becomes much less complex and costly, hence more attractive. Because more stringent noise regulations are being imposed for certification of commercial and business aircraft, it is important that the noise suppressor system be efficient, yet attractive by its simplicity, reliability, low cost, and yet has aircraft performance enhancement capability.
A first objective of the exhaust nozzle disclosed hereinbelow is to overcome drawbacks in previous jet engine nozzles, and have variable exhaust area capabilities, for turbofan engines installed on business or commercial aircraft with short, long, or C-duct nacelles, that may or may not be equipped with a thrust reverser.
A second objective of the exhaust nozzle, for the case the nacelle is equipped with a thrust reverser, is that it can be combined with any type of reverser: fan reversers, pivoting door or target reversers.
A third objective of the exhaust nozzle, for the case the nacelle is equipped with a thrust reverser, is to allow the adjustment of the value of the throat of the exhaust nozzle independently from the thrust reverser components.
A fourth objective of the exhaust nozzle is to allow automatic full opening of the exit area of the exhaust nozzle from sea level to a pre-set altitude, and automatic full closing above the pre-set altitude.
A fifth objective of the exhaust nozzle is to reduce the noise generated by the jet exhaust at aircraft take-off.
A sixth objective of the exhaust nozzle is to optimize the performance of the engine for all phases of the flight.
Yet another object of the exhaust nozzle is to have minimal delta-weight, as well as minimal cost compared to a fixed nozzle.
While the variable exhaust area nozzle for turbofan engines disclosed hereinbelow can be installed on any type of nacelle, long, short, or C-duct, with or without thrust reversers, other objects, characteristics and advantages will become apparent from the detailed description.
A gas turbine engine exhaust nozzle includes coaxial inner and outer conduits. The inner conduit has a main outlet at an aft end thereof, and a row of radial apertures spaced upstream from the outlet. The outer conduit has an auxiliary outlet at an aft end thereof, and surrounds the inner conduit over the apertures to form a bypass channel terminating at the auxiliary outlet. A plurality of flaps are hinged at upstream ends thereof to selectively cover and uncover corresponding ones of the apertures and selectively bypass a portion of exhaust flow from the inner conduit through the outer conduit in confluent streams from both the main and auxiliary outlets.